[r] R - " missing value where TRUE/FALSE needed "

I'm trying to execute the following code in R

comments = c("no","yes",NA)
for (l in 1:length(comments)) {
    if (comments[l] != NA) print(comments[l]);
}

But I'm getting an error

Error in if (comments[l] != NA) print(comments[l]) : missing value where TRUE/FALSE needed

What's going on here?

Can you change the if condition to this:

if (!is.na(comments[l])) print(comments[l]);

You can only check for NA values with is.na().